Radio receiver



June 29,1937. P, F, Q HOLST 2,085,430

RADIO RECEIVER Filed April 28, 1934 '14g 5 r i 17 7;/1 15 S500/v0 5575070@ @Miei/fm@ Patented June 29, 1937 UNITED STATES PATENT OFFICE Corporation of America,

Delaware a corporation of Application April 28, 1934, Serial No. 722,835

8 Claims.

The present invention relates to radio receivers, and more particularly, to radio receivers wherein stray electrical fields from sources, such as grounded circuit returns which convey relatively heavy vibratory or pulsating currents, tend to set up interference noises by coupling with sensitive audio frequency circuits.

In radio receivers for automobile and portable installations, the currents in the metallic chassis 10 of the receiver from the supply source are necessarily high because of the low voltage battery source of supply forming part of the starting and ignition system. Vibratory rectifier or power supply devices, adapted to operate in connection with a low voltage power supply source to provide the necessary anode potentials for a radio receiver,

may set up, in the chassis of the receiver and in the vehicle wiring connected with the battery, vibratory signal or current waves which enter the audio frequency amplifier system and interfere with the normal and proper operation of the receiver.

One of the major difficulties, experienced in the design and construction of automobile receivers,

includes that of reducing the noise level resulting from so-called hum pick-up, from such sources as the vibrator or power supply unit and from the ignition apparatus of the vehicle.

It is, therefore, an object of the present invention to provide an improved radio signal receiving circuit for eliminating hum pick-up or audio frequency interference from stray electrical fields originating in chassis currents and the like.

It has been found that interference from stray fields set up by heavy chassis currents in a radio receiving apparatus may be eliminated by proper design of the interstage coupling transformer means just preceding the audio frequency detector, which, in a superheterodyne receiver, is the second detector and the audio frequency point of greatest sensitivity. As is well understood, and as used herein, an audio frequency detector is one which is provided with an audio frequency output 4.5 circuit and which is usually followed by an audio frequency amplifier.

Accordingly, itis a further object of the present invention to provide an improved input coupling means and circuit for an audio frequency detector. The usual second detector may be in the form of a diode rectifier having an untuned input circuit constituted by an untuned secondary of a coupling transformer. 55k It is also an object of the present invention to (Cl. Z50-20) provide an improved input coupling system for a diode rectifier for audio frequency detection.

It is a still further object of the present invention to provide an improved input coupling transformer for audio frequency detectors and the like, 5 which is effective to prevent picking up audio frequency disturbances from stray vibratory or pulsating electrical fields about or in the apparatus chassis, and other surrounding circuit elements. Such fields may result from pulsating or 10 Vibratory electrical supply currents flowing in the chassis as a circuit return element. In a radio receiver, adapted for use in automobiles and similar vehicles, the ability to prevent stray hum and interference pick-up includes disturbances ordinarily encountered in connection with the operation of ignition apparatus.

It is also a further object of the invention to provide an improved input circuit and coupling means therefor for an audio frequency detector. 20

It is an object of the present invention to provide arr improved transformer for use in a superheterodyne receiver between the intermediate frequency amplifier and the second detector.

It is also a further object of the present inven- 25 tion to provide an improved audio frequency detector input circuit and coupling means therefor, for radio receiving apparatus and the like, for preventing audio frequency interference from entering the audio frequency system at the most sensitive point therein.

In accordance with the invention, the input circuit of a detector device, such as a second or audio frequency detector of a superheterodyne receiver, is constituted by the secondary of a coupling transformer, one half of which is spaced from the primary and the other half of the Secondary sufficiently to reduce the coupling thereof with the primary at signal frequencies to substantially a minimum, while retaining a physical relation therewith, such that both halves of the secondary winding are always in the same field of disturbance at audio frequency. The two halves of the secondary are connected or arranged in opposite phase relation to each other, whereby voltages induced in the secondary by interference waves and currents at audio frequencies, are neutralized and balanced out of the input circuit. 50

The invention will, however, be better understood from the following description when considered in connection with the accompanying drawing, and its scope will be pointed out in the appended claims. j

of and terminal lead connections for the wind-- ings of said transformer.

Referring to Figure l, a detector device 5 is connected with an amplifier device 6 throughv coupling means indicated at 'I. The detector device 5 represents any audio frequency detector for radio receiving apparatus and the like and, in the present example, is provided as the second detector of a superheterodyne receiver. The detector, furthermore, is of the diode rectifier type, comprising a heated cathode B and two diode plates or anodes 9 associated therewith. In common with the cathode 8, the device E also includes,in the same envelope with the diode rectiiier, a grid electrode Il] andan output II as an amplifier device, the connections for which will hereinafter be described. l

The amplier device B represents any suitable source of signal potentials for application to the detector device 5 and, in therprresent example, represents the last stage of an intermediate frequency amplifier, being coupled with a preceding stage (not shown) through a tuned interstage coupling transformer i2. Both the primary and the secondary of the transformer i2 are tuned to a desired intermediate frequency, kc., for

example.

The coupling device l' includes a coupling transformer i3 having a primary winding I4 and a secondary winding I5 together with a third or tertiary winding i6 in series with the secondary winding I5, and the primary winding lli, preferably in a shielded container indicated by the dotted lines il. The secondary and tertiary windings may be considered as a divided secondary winding or one winding having two substantially equal parts. The primary winding is also provided witha shunt tuning condenser ILB by which it is tuned Vto the desired intermediate frequency.

The secondary winding 'I5 is connected preferably, at itsV high potential end, with at least one and. in the present example, withtwo, of

the diode or plates Q through'a signal input cir cuit for the detector indicated at I9. The circuit is completed through the third or tertiary winding i6 connected directly with the low potential end of the secondary I5 as indicated at 20, and by a cathode return lead 2|, between which, and the tertiary winding I6 is interposed in circuit, a filter impedance element 22 and potential drop producing element Y23. The filter, including the element 22, is completed byl a shunt by-pass condenser 24 to the cathode lead The potential drop producingl volume control element 23 is provided with a'variable volume control tap 25, which is coupled throughacoupling condenser 2t and a coupling impedance 2 with the grid electrode l0 of the device 5, a shielded lead; 28 being provided fori connection with the grid. The cathode return lead is provided with a self bias resistor and a shunt ley-pass condenser 3i) therefor. Both impedancesl 21 vand 29 are grounded as indicated at 3E, whereby po tentials existing in the resistor 29 are applied to theV grid It as a'bias potential therefor.

It will be seen that the secondary winding i5 of the coupling transformer i3 is connected with the input electrodes of the detector through the third or tertiary winding I6 in the low potential or cathode side of the input circuit, and that the primary Winding Hl is coupled with the secondary through the one winding IES.

The direct current components of signals rectified through the action of the diode rectifier 8 9 flow through the impedance elements 22 and 23 and resulting direct current potentials derived from tap points 33 and 3d are supplied for automatic volume control purposes to Ycontrol circuits indicated at 35. As the automatic vol- .ume control system does not concern the invention, further description of the same is not believed to be necessary.

The audio frequency component of the rectifier signal is derived from the impedance element 23 and is applied to the control grid Ii] through the coupling elements 26 and 2i. The triode portion of the device 5 functions as an audio frequency amplier, and audio frequency` scribed and shown, are' taken from an anode supply lead fili and the anode circuits are rturned to ground or chassis through ground connections indicated at 4|.

The power supply means, inthe present example, is a vibratory unit #i2 connected with the high voltage +B' lead t0 and an input supply Y lead 43 leading to any suitable low voltage source of current such as a six volt supply as indicated, one side of the supply line being grounded as indicated at 4t. The vibratory power supply unit is also connected with the low voltage supplyy source and with the chassis through a ground connection indicated at 45.

The vibrator supply unit draws a relatively high current from the six volt supply source and, since the same is of a pulsating or vibratory nature withinY the audio frequency range, audio frequency circuits in the apparatus may become the source of laudio frequency interference voltages because of'induced currents in such circuits.

The detector input'circuit in the case of a di-Y ode rectifier is preferably'untuned, as indicated, and, for that reason, the winding I5 is relatively large in number of turns. For example, for 175 kc., the primary winding I4, may comprise 1200k Yularly true in automobile installations employing a vibrator power supply unit connected as shown, to'supply the anode circuits, and closely asso# ciated with the receiving apparatus.

To eliminate the effect of alternating or vibratory stray fields such as caused by vibratory supply currents of relatively large magnitude in the receiving apparatus, the secondary winding I5 is provided with the additional or tertiary winding I6 in association therewith, but indirectly coupled with the primary winding Iii. Furthermore, the winding i6 is connected in circuit and associated with the secondary winding I5 in opposite 4phase relation thereto, whereby it forms a bucking winding for the transformer i3 and, in practice, is mounted on the same winding form with the coils constituting the primary Id and the secondary I5.

The physical arrangement of the coils or windings indicated in Figure 2 and, for identifying the coils, the same reference numerals are applied thereto as in Figure 1.

Referring to Fig. 2, it will be seen that the pri-V mary winding Iii and secondary winding I5 are electrically closely coupled and mounted substantially coaXially on a winding form or bobbin 46. The latter is supported at one end on a bracket member il secured to a screw-threaded base member 18. The bracket 4l also serves to support an insulating base 49 for the tuning condenser I8.

The base member 48 is of thin sheet material, and cooperates with a detachable cover member 5I to provide a shielding container for the transformer unit. The end of the bobbin 45, opposite to the bracket lll, is supported within the container by a thin sheet of insulating material 52 which is mounted on the bobbin 36 in a plane at a right angle to the axis thereof and is arranged to engage at its edges with the inner walls of the cover 5l substantially as indicated in Fig. 2.

The bracket l is secured to the base member @8 by suitable rivets 53 having screw-thread projecting ends 551 by which the unit is nally mounted in an apparatus. The bracket furthermore is bent, as indicated, to enter the lower end of the bobbin 13.6 which is preferably of wood and to hold the same above the condenser I8 in spaced relation thereto and centrally of the container.

The condenser and the bobbin i6 are of such length axially that the tertiary winding I6 may be mounted on the same winding form or bobbin i6 but substantially spaced from the secondary l5 and the primary Ill that the electrical coupling at signal frequencies, such as the intermediate frequency, is substantially negligible. At the same time, the physical relation or spacing between the coils is sufficient to permit both to lie in the same stray interference fields, whereby equal potentials are induced thereby into both of the windings I5 and I6. If the potentials are equal, since the coils are connected in opposite phase relation, the effect upon the circuit is substantially zero and the interference from audio frequency sources is substantially eliminated.

In a practical construction, the coils I5 and I6 are preferably of the same size and the same number of turns, although any suitable coil arrangement may be employed which provides for equal voltages being generated in both coils in response to stray interference currents or elds.

With the use of a tertiary winding I6 in series with the secondary winding i5, it has been found that each half of the secondary for kc. intermediate frequency, that is, the secondary and the tertiary windings may each have approximately 800 turns in universal coils of the size substantially as shown in Fig. 2, while the primary winding may comprise approximately 1200 turns in a universal coil substantially of the size indicated in Fig. 2.

The three coils are preferably wound directly on the bobbin 46 at the same time, and for that reason, are all wound in the same direction; the two windings I5 and I6 being broken after 800 turns are completed, and the winding I4y continuing thereafter until the 1200 turns are completed. A considerable saving of manufacturing cost is thereby effected and the opposite phase relation between the windings I5 and I6 is provided by connecting the coils in opposite phase relation by interconnection of proper terminal leads, as shown in Fig. 3, to which attention is now directed.

Referring now to Fig. 3, wherein the same reference numerals have been applied to the three windings thereby to identify them with the preceding figures, the inner and outer leads of the windings I6, I5, and I4 are indicated on the drawing. It will be seen that the inner lead of the tertiary winding I6 is connected with the inner lead of the secondary winding l5. These leads are indicated at 55 in Fig. 2 and are connected with suitable terminals (not shown) but corresponding to the terminals 56 for the primary leads indicated at 51. The outer lead of the winding I5 is connected to the diode.

By connecting the coils, as indicated in Fig. 3, the magnetic and capacity coupling between the primary Iii and secondary I5 are both aiding, and the secondary winding I5 and the tertiary winding i6 may be arranged in opposite phase relation although wound in the same direction on the same winding form.

From the foregoing description it will be seen that stray vibratory currents or iields in or associated with the chassis of receiving apparatus may substantially be prevented from causing interference b-y preventing such fields and currents from setting up potentials in the audio frequency detector input circuit and that this may not be prevented by shielding alone. The means which has been provided for effecting magnetic and capacity coupling with the primary winding as an input circuit for the detector has been found to effectively prevent audio frequency interference of this type and has been applied to automobile receivers having vibratory power supply means with highly satisfactory results.

I claim as my invention:

1. In a radio receiving system, the combination with a high frequency signal circuit and an audio frequency detector having a signal input circuit, of a coupling transformer unit for said circuits comprising three universal windings arranged in coaxial relation to each other, two of said windings being electrically equal and connected in opposite phase relation to each other in the detector input circuit, and the third winding being a signal input winding in said high frequency signal circuit providing a transformer primary associated in close coupled relation to one of said two windings while having substantially minimum coupling with the other of said windings.

2. In a radio receiving system, the combination with a diode rectifier device providing a signal detector, of transformer means for preventing electrical disturbances about said diode rectifier device from creating interference signals in the rectifier output circuit, said means comprising a tuned primary winding, and an untuned secondary Winding', adapted for connection with said diode rectifier device, and comprising tWo sections arranged in spaced relation With each other and connected in opposite phase relation, and one of said winding sections being `closely associated with the primary Winding.

nected together, and that the diode rectifier device is provided with an anode and a cathode which are connected with the outer ends of said winding sections.

5. In a superheterodyne receiver, the cornbination with an intermediate frequency amplier and a second detector, of an interstage coupling device therefor, comp-rising a transformer unit having a tuned primary winding in circuit with said intermediate frequency amplifier, a secondary Winding in circuit with said second detector and electrically coupled. With said primary Winding for transmitting signals from said amplifier t0 said detector at intermediate frequencies, and a third winding associated With 'the secondary Winding in spaced relation to the primary Winding and in opposite phase relation to the secondary Winding for applying, in circuit with said secondary Winding a potential substantially equal and opposite in phase to a potential set-up in said secondary winding by stray audio frequency currents and iields in said receiver. Y

V6. The combination with an electronic tube amplifier and a Vibratorypower supply unit therefor, of a signal detector device, and signal input coupling means therefor comprising a secondary winding, a tertiary Winding connected in circuit and associated with said secondary Winding in opposite phase relation thereto, a signal input circuit for said detector device including said windings, and a primary Winding connected with said amplier and more closely electricallyA coupled to the secondary winding than to the tertiary Winding.`

'7. In a radio receiver, means operative to create audio frequency disturbances therein, the combination 'with a diode detector device, of an yinput coupling transformer therefor, comprising an untuned secondary Winding connected with the diode anode, a tertiary Winding associated with said rst Winding in series therewith, and connected in opposite phase relation thereto, and means for'supplying signals to said secondary winding substantiallyrto the eX- clusion of the tertiary Winding.

8. In an automobile radio receiving system, the combination with an anode Voltage supply means adapted for low voltage operation, and characterized by the fact that it generates audio frequency stray currents andV elds in said system, of a detector input circuit adapted for minimizing the effect of such currents and fields, and comprising a transformer having a secondary winding connected With the detector, a tertiary Winding associated therewith in opposite phase relation thereto in circuit with said de- Y tector, and a prmary winding magnetically and capacitively coupled to said secondary winding in aiding phase relation more closely than 4to said tertiary Winding. Y Y Y' i POUL F. G. HOLST. 

